The present invention relates generally to turbofan aircraft engines, and, more specifically, to exhaust nozzles therefor.
A typical turbofan aircraft engine includes a fan powered by a core engine. The core engine includes a surrounding cowl or nacelle, and the fan includes a corresponding cowl or nacelle at the forward end of the core engine which extends aft either in part or fully thereover.
The fan nacelle is spaced radially outwardly from the core nacelle to define an annular bypass duct therebetween. During operation, the core engine powers the fan which pressurizes ambient air to produce propulsion thrust in the fan air bypassing the core engine and discharged from the fan exhaust nozzle.
A portion of the fan air is channeled into the core engine wherein it is pressurized and mixed with fuel for generating hot combustion gases. Energy is extracted from the combustion gases in high and low pressure turbines which in turn power a compressor and the fan. The core exhaust gases are discharged from the core engine through a core exhaust nozzle and provide additional thrust for propelling the aircraft in flight.
In a typical short fan nacelle, the fan nozzle is spaced upstream from the core nozzle, and the fan exhaust is discharged separately from and surrounding the core exhaust. In a long nacelle, the fan nacelle extends aft of the core nozzle to provide a single common nozzle through which both the fan bypass air and core exhaust are discharged from the engine.
The fan nozzle and the core nozzle are typically fixed area nozzles, although they could be configured as variable area nozzles. Variable area nozzles permit adjustment of the aerodynamic performance of the engine which correspondingly increases complexity, weight, and cost of the nozzle.
Furthermore, turbofan aircraft engines typically include thrust reversers for use in providing braking thrust during landing of the aircraft. Various types of thrust reversers are found in the engine nacelle and further increase complexity, weight, and cost of the engine.
In U.S. Pat. No. 6,751,944; and entitled “Confluent Variable Exhaust Nozzle,” assigned to the present assignee, and incorporated herein by reference, an improved variable area exhaust nozzle is disclosed for a turbofan aircraft engine. The confluent nozzle includes outer and inner conduits, with a plurality of flaps therebetween. The flaps may be selectively opened to bypass a portion of exhaust flow from the inner conduit through the outer conduit in confluent exhaust streams from concentric main and auxiliary exhaust outlets.
In this way, the auxiliary outlet may be operated during takeoff operation of the aircraft for temporarily increasing exhaust flow area for correspondingly reducing velocity of the exhaust flow. Noise may therefore be reduced during takeoff operation using a relatively simple and compact variable area configuration.
However, the typical thrust reverser includes thrust reversing cascade vanes mounted at the axial splitline or joint between a fixed forward cowl and a translating aft cowl. A main actuator deploys aft the aft cowl during landing for reversing exhaust thrust and braking the aircraft on the runway.
The variable exhaust nozzle is mounted in the aft cowl and includes a secondary actuator for controlling its operation during engine takeoff. Whereas the variable nozzle operates during aircraft flight with the aft cowl retracted, the thrust reverser operates only during landing with the aft cowl deployed.
Deployment of the aft cowl opens the joint with the forward cowl to expose the cascade vanes, and would therefore require sufficient length and slack in the power and electrical control lines for the variable nozzle. The power and control connections to the variable nozzle must be sufficiently durable and redundant for long life, which would therefore increase the complexity and cost thereof for bridging the intercowl joint during the repeated opening and closing thereof required every time the aircraft lands.
Accordingly, it is desired to provide an improved power and control system for the variable area exhaust nozzle in a turbofan aircraft engine having a thrust reverser therein.